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ps1a - MIT Biology Department 7.012 Introductory Biology...

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Name __________________________ TA____________ Section ____ 7.012 Problem Set 1 Solutions Question 1 A. a) Explain what an ion is. An ion is an electrically charged particle that forms when an atom gains or loses one or more electrons. b) Explain what a van der Waals force is. A weak attraction between molecules resulting from a momentary shift of the electron density in a molecule thus establishing a dipole moment. The dipoles induced by the effect of one molecule on the others lead to a net electrostatic attraction. c) Match the atoms and molecules listed below with the appropriate descriptive. Choose from: cation anion polar non-charged nonpolar non-charged Cl - Anion H 2 O Polar non-charged Na + Cation CH 4 Nonpolar non-charged d) Circle the “side chain” in each of the amino acids given below . C C O O H NH 3 CH 2 CH 2 O O C - + - GLUTAMIC ACID C C O O H NH 3 CH 2 CH 2 CH 2 CH 2 NH 3 + - + LYSINE C C O O H NH 3 CH 2 OH H H H H - + TYROSINE ASPARAGINE C C O O H NH 3 CH 2 C O NH 2 - + C C O O H NH 3 H - + GLYCINE C C O O H NH 3 CH 2 CH 2 O C NH 2 - + GLUTAMINE MIT Biology Department 7.012: Introductory Biology - Fall 2004 Instructors: Professor Eric Lander, Professor Robert A. Weinberg, Dr. Claudette Gardel
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2 e) Check the following terms to describe the side chains of the amino acids you circled above. Side Chain of… Charged Non Charged Polar Non Polar Hydrophobic Hydrophilic Glutamic Acid Lysine Tyrosine -/+ -/+ -/+ Asparagine Glycine Glutamine f) Explain why ethane (C 2 H 6 ) is a non-polar molecule while ethanol (C 2 H 5 - OH) is a polar molecule. (A diagram of each molecule may help.) Ethanol is a polar molecule because there is a partial charge separation associated with the bond between the hydrogen and the oxygen. The higher electronegativity of oxygen pulls the electrons
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